The present invention relates to a magnetic tape cassette such as a digital video cassette (DVC) or the like.
Generally, in an audio apparatus, a video apparatus and the like, there are in many cases used magnetic tape cassettes of a structure that a magnetic tape wound around a pair of tape reels is held inside a cassette case so as to run for conducting recording and reproducing.
FIG. 12 is an exploded perspective view of the DVC which is one example of the magnetic tape cassette. The magnetic tape cassette 50 comprises an upper cassette half 2 and a lower cassette half 3 each of which has a flat plate and peripheral walls. These upper and lower cassette halves 2, 3 are assembled and fastened by means of a plurality of screws. A pair of tape reels 1 which are formed by welding their upper flanges with their lower flanges are rotatably supported in the lower cassette half 3 in a state where a magnetic tape 47 is wound around the tape reels 1.
There are provided tape guides 14 at both sides of an opening 5 which is formed at a front end side (a lower side in the drawing) of the lower cassette half 3. Each of the tape guides 14 is adapted to guide the magnetic tape 47 which is fed from one of the tape reels 1 and taken up by the other tape reel and to pass the magnetic tape 47 at a determined position corresponding to the opening 5.
A tape reel locking member 16 having a tape reel locking arm 15 is assembled to a rear end side (an upper side in the drawing) of the lower cassette half 3. The tape reel locking member 16 is biased by means of a compression coil spring 17 so as to engage the tape reel locking arm 15 with an engaging tooth which is formed at an outer circumference of the lower flange of each of the tape reels 1 thereby to block an accidental rotation of the tape reel 1. A slackened winding of the magnetic tape 47 can be prevented with this arrangement.
To the flat plate 4 of the upper cassette half 2 are fitted reel pressing leaf springs 48 for the respective tape reels 1. Each of the reel pressing leaf springs 48 is supported by the upper cassette half 2 in a cantilever manner so as to push the corresponding tape reel 1 toward the lower cassette half 3. Further, the flat plate 4 of the upper cassette half 2 is provided with an opening which extends in a transverse direction of the flat plate 4 at one side of the flat plate 4 in its longitudinal direction (a right hand in the drawing) so that an amount of winding of the magnetic tape 47 on the tape reels 1 can be confirmed. A transparent window member 49 is fitted so as to close the opening.
To a front end side of the upper cassette half 2 are freely and openably fitted an outer lid 20, a top lid 21 and an inner lid 22 for covering a front and a back faces of the magnetic tape 47 which is stretched between a pair of the tape guides 14 in the lower cassette half 3, in order to obtain such a dust proofing property as durable for an outdoor use.
FIG. 13 shows one of the tape guides 14 which are provided in the lower cassette half 3 and shown in FIG. 12. Generally, the tape guide is uprightly provided on the flat plate of the lower cassette half. In this case, a hollow, that is, cylindrically formed tape guide 14 is integrally formed on the flat plate 10 of the lower cassette half 3. The tape guide 14 includes a curved portion 30 with which the magnetic tape 47 slidably contacts, and flat portions 31a, 31b at a rear end side (an upper side in the drawing) and at an inner side (a left hand in the drawing) of the tape guide respectively with which the magnetic tape 47 does not contact. In this case, the tape guide 14 is formed in such a manner that a thickness of the tape guide 14 is substantially constant in a circumferential direction, and therefore, the curved portion 30 and the flat portions 31a, 31b are substantially equal to each other in thickness.
When the lower cassette half 3 is formed by molding, a molten resin introduced into a mold fills at first a cavity for the flat plate 10. Then, the molten resin flows into cavities for the tape guides 14 connected to the cavity for the flat plate 10 and into cavities for other members.
There has been sometimes formed a weld line (hereinafter referred to as xe2x80x9ca weldxe2x80x9d) W on a surface of the curved portion 30 of the tape guide 14 as shown in FIG. 14, when the lower cassette half 3 of the above described magnetic tape cassette 50 is molded. In addition, a pock v of an air bubble which is generated when the air bubble is discharged has been also formed in some cases on the surface of the curved portion 30. There is a fear that such a weld W or an air bubble pock v may damage the magnetic tape if they are formed on the surface of the curved portion 30 with which the magnetic tape slidably contacts.
The term xe2x80x9cweldxe2x80x9d means herein a thin line which is formed at a portion where two or more streams of the molten resin join, and the term xe2x80x9cair bubblexe2x80x9d means a hollow spot which is formed inside a molded article.
A first object of the invention is to provide a magnetic tape cassette which is free from molding defects on the surface of the curved portion of the tape guide with which the magnetic tape slidably contacts.
FIG. 15 shows a manner of placing the window member 49 on the flat plate 4 so as to close the opening formed in the flat plate 4, when the window member 49 shown in FIG. 12 is welded to the flat plate 4 of the upper cassette half 2. As shown in FIG. 15, this work is generally conducted by hand.
An inner face (an upper face in the drawing) of the flat plate 4 of the upper cassette half 2 is formed at a peripheral part of the opening with a stepped flat face 35a (hereinafter referred to as xe2x80x9ca window supporting facexe2x80x9d) which is recessed from other parts of the inner face of the flat plate. The window supporting face 35a supports the peripheral edge of the window member 49, when the window member 49 is placed on the flat plate 4. A side face 35b between the inner face of the flat plate 4 and the window supporting face 35a is formed in a tapered shape which serves as an introducing face for guiding the window member 49 to the window supporting face 35a. 
FIG. 16 shows a sectional view taken along a line Yxe2x80x94Y in FIG. 15 in a state where the window member 49 has been placed on the flat plate 4. As shown in FIG. 16, a peripheral wall (a back end wall) 7 of the upper cassette half 2 is provided at its outer face with a recess 7a to which a label is to be attached. A peripheral edge of the window member 49 is arranged close to an inner face of a base portion of the peripheral wall 7.
A part of an outer face (a lower face in the drawing) of the window member 49 which is supported by the window supporting face 35a is in a form of a stepped flat face 49a (hereinafter referred to as xe2x80x9ca supported facexe2x80x9d) which is recessed from other parts of the outer face of the window member. The supported face 49a is projectingly provided with a welded rib 49b in a shape of a triangle in section, which is adapted to abut against the window supporting face 35a of the flat plate 4 when the window member 49 is placed on the flat plate 4.
FIG. 17 shows another upper cassette half 52 which has been conventionally used. The flat plate 4 of the upper cassette half 52, similarly to the upper cassette half 2 shown in FIG. 16, has the window supporting face 35a, and the side face 35b connecting the inner face of the flat plate to the window supporting face 35a is formed in a tapered face. A positioning rib 45 having a side face which is vertical with respect to the inner face of the flat plate is formed at the inner face of the base portion of the peripheral wall 7. In such an upper cassette half 52, the window member 49 can be accurately positioned on the flat plate 4 without affecting its mountability, by precisely forming the side face of the positioning rib 45.
In order to weld the window member 49 to the flat plate 4 of the upper cassette half 2 as shown in FIG. 16, when the window member 49 is placed on the flat plate 4 and released from the hand, the window member 49 sometimes adheres to the hand by static electricity, etc. and floats up from the flat plate 4, as shown by a two-dot chain line in FIG. 18. In case where the window member 49 is released from the hand in the air, an accurate positioning of the window member 49 on the flat plate 4 may be sometimes impossible, so that the supported face 49a of the window member may ride on the inner face of the flat plate, as shown by a solid line in FIG. 18, for example.
Also in case where the window member 49 is placed on the flat plate 4 of the upper cassette half 52 as shown in FIG. 17, when the window member 49 is released from the hand, the window member sometimes adheres to the hand and floats up from the flat plate 4 as shown by a two-dot chain line in FIG. 19. When the window member 49 is released from the hand in the air, the supported face 49a of the window member may sometimes tide on the upper face of the positioning rib 45 as shown by a solid line in FIG. 19.
As described above, the work for accurately positioning the window member 49 on the flat plate 4 has been very annoying, and an improvement of the work has been required.
A second object of the invention is to provide a magnetic tape cassette in which the window member can be easily placed on an accurate position of the flat plate, when the window member is fitted to the flat plate of the upper cassette half.
As shown in FIG. 20, at a corner part of the rear end wall 7 of the upper cassette half 2, is formed an opening 34 for exposing a safety lug for preventing a wrong erasure of recorded data on the magnetic tape. Moreover, at a corner part of a rear end wall 11 of the lower cassette half 3 are formed openings 37 for exposing contacts of an ID board for identifying a type and a use of the magnetic tape.
FIG. 21 is a plan view of the ID board. The ID board 33 has a plurality of (four in FIG. 21) contacts 36 which are exposed through the openings 37 formed in the lower cassette half. Signals concerning the type and the use of the magnetic tape are exchanged between the ID board and a recording and reproducing apparatus (a hardware) by way of the contacts 36. The ID board is manufactured through the following steps:
First of fall, a copper foil is applied to a printed circuit board 38 formed of a substrate material such as a glass reinforced epoxy resin or the like, and after a desired pattern has been printed (etched) on the board, the copper foil is removed from unnecessary parts thereby to form the copper foil of a desired shape (rectangular in FIG. 21) which constitutes the contacts 36. Then, after the printed circuit board 38 is rinsed, the copper foil is plated with gold. Plating the copper foil with gold is an indispensable treatment for preventing a faulty detection due to repeated sliding motions of the ID board with respect to the hardware. Finally, by stamping by means of a stamping die, the printed circuit board 38 is formed in such a desired shape (flat plate like and substantially L-shaped in FIG. 21) as the printed circuit board 38 can be received in the lower cassette half.
There has been a problem that on occasion that the printed circuit board 38 of ID board 33 is stamped on the stamping die, a minute burr 39 may be created at an end face of each of the contacts 36 of the printed circuit board 38 in a direction of an arrow B in FIG. 22, and partial damages 40 or the like may be caused on the gold plating on the copper foil by the burr 39. When the burr on the gold plating and the partial damages 40 or the like have occurred, there has been a fear that while the magnetic tape cassette 50 is repeatedly inserted into and removed from the hardware 43 as shown in FIG. 23, the burrs may be spread further to reach to an insulating part, or a broken piece may adhere to the insulating part to cause a short of the printed circuit board 38.
A third object of the invention is to provide a magnetic tape cassette in which the partial damages of the plating on the contacts due to the minute burrs in the ID board can be reliably avoided, whereby a short of the circuit board of the ID board can be reliably prevented.
As shown in FIG. 12, the upper cassette half 2 of the magnetic tape cassette 50 includes the flat plate 4, the rear end wall 7, the front end wall 6 having the opening 5, and a left and a right side walls 8 which are positioned at outermost sides in a longitudinal direction of the upper cassette half 2. The lower cassette half 3 includes the flat plate 10, the rear end wall 11, the front end wall 13 having the opening 5, and a left and a right side walls 12 which are positioned at outermost sides in a longitudinal direction of the lower cassette half 3. The outer lid 20 includes a lid front face 23 and two lid side faces 24. The top lid 21 includes a lid upper face 25 and two lid side faces 26. The top lid 21 has an inner lid 22 rotatably fitted thereto.
FIG. 24 is a perspective view of an assembled product of the magnetic tape cassette 50. FIG. 24A is an overall view of the assembled product, FIG. 24B is an enlarged view of an encircled part A in FIG. 24A.
FIG. 25 is a plan view of the assembled product of the magnetic tape cassette 50 as shown in FIG. 24. FIG. 25A is an overall view of the assembled product, and FIG. 25B is an enlarged view of an encircled part B in FIG. 25A.
Longitudinal dimensions of the outer lid 20 and the top lid 21 are slightly smaller than a longitudinal dimension of the cassette case consisting of the upper cassette half 2 and the lower cassette half 3 assembled together. As shown in FIG. 25B, the end walls 8, 12 of the cassette case extend outwardly (leftward and rightward in FIG. 25) beyond the lid side faces 24, 26 in a longitudinal direction of the cassette case. They are thus designed so that the outer lid 20 and the top lid 21 may not project beyond the side walls 8, 12 of the cassette case, even though the outer lid 20 and the top lid 21 move in the longitudinal direction to be displaced toward one side by an amount Di of the displacement, when the magnetic tape cassette 50 is loaded in the hardware. With this design, the loading of the magnetic tape cassette 50 in the hardware can be smoothly conducted.
However, because the cassette case is so constructed as to project in the longitudinal direction beyond the lids as described above, in case where a user unintentionally happens to load the cassette 50 inclinedly in the hardware, front edges 28 of the projecting side walls 8, 12 of the cassette case may sometimes collide against a cassette loading mouth in the hardware. Moreover, when the cassette is forced to be loaded, the front edges 28, the outer lid 20 and the inner lid 21 will be caught inside the cassette loading mouth and can not be taken out of the hardware in the worst case.
A fourth object of the invention is to provide a magnetic tape cassette which can be smoothly loaded in the recording and reproducing apparatus, even in case where the user unintentionally happens to load the cassette inclinedly in the recording and reproducing apparatus.
The inventors of the invention have earnestly studied and found out that the above described first object can be attained by making the thickness of the curved portion of the tape guide larger than the thickness of the other parts such as the flat portions.
A magnetic tape cassette according to the invention comprises a lower cassette half having tape guides integrally formed therewith and an upper cassette half assembled to the upper cassette half to form a cassette case, a pair of tape reels around which a magnetic tape is wound being rotatably supported inside the cassette case, the magnetic tape being guided by the tape guides so as to run at a determined position, and is characterized in that each of the tape guides includes a cylindrical part having in its circumferential direction a curved portion with which the magnetic tape slidably contacts, the curved portion having a thickness larger than those of other circumferential portions of the cylindrical part.
In the magnetic tape cassette of the above described structure, molding defects will not happen on a surface of the curved portion of the tape guide, when the upper cassette half is molded.
Because the conventional tape guide has been formed in such a manner that the curved portion and the other portions such as the flat portions are substantially equal to each other in thickness, the molten resin has filled the cavity for the flat portion first of all at molding, and the streams of the molten resin flowed from both circumferential sides have sometimes joined in the cavity for the curved portion. In such case, the welds or the like have been formed on the surface of the curved portion of the tape guide.
According to the invention, because the thickness of the curved portion is larger than the thickness of the other portions such as the flat portions, and the molten resin fills at first the cavity for the curved portion which is wider and easier to receive the flow, and then fills the cavities for the flat portions. Accordingly two streams of the resin will not join in the cavity for the curved portion so that occurrence of the welds or the like can be prevented.
According to the invention, the thickness of the curved portion of the tape guide may be larger than the thickness of the other portions in circumferential direction of the tape guide, and the thickness of the curved portion is preferably one and a half (1.5) to three (3) times as large as the thickness of the other portions. With this design, the occurrence of the molding defects on the surface of the curved portion will be more remarkably prevented.
The second object of the invention can be attained by a magnetic tape cassette which comprises an upper cassette half having a flat plate provided with a peripheral wall and an opening, a window member of a separate body being fitted to the upper cassette so as to close the opening, and a lower cassette assembled to the upper cassette half to form a cassette case, a pair of tape reels around which a magnetic tape is wound being rotatably supported inside the cassette case, characterized in that the peripheral wall is provided with a positioning rib which extends from a base portion of the peripheral wall up to a position higher than a half of a height of the peripheral wall, the positioning rib being adapted to abut against a part of a circumferential edge of the window member.
In case where the positioning rib does not extend up to the half of the height of the peripheral wall from the base portion of the peripheral wall, the window member is likely to adhere to the hand and float up when the window member is released from the hand, and when the window member is released from the hand in the air, the window member will not be placed at the accurate position on the flat plate in some cases.
In the magnetic tape cassette of the above described structure, when the window member is fitted to the flat plate of the upper cassette half, the window member can be easily placed at the accurate position on the flat plate.
In case where the window member is fitted to the upper cassette half of the magnetic tape cassette of the above described structure, when the window member is released from the hand after it has been placed on the flat plate, it is preferable to slide the fingers or the like which are in contact with the window member along the window member by withdrawing the hand toward the peripheral wall which is provided with the positioning rib. With this motion, the window member can be prevented from floating up from the flat plate.
The peripheral wall of the upper cassette half may be provided with a plurality of positioning ribs, but even a single positioning rib can fully achieve the function.
According to the invention, the height of the positioning rib is a half or more of the height of the peripheral wall and the same or less as the height of the peripheral wall. A difference in height between the peripheral wall and the positioning rib is preferably 2 mm or less. With this design, the window member can be more reliably placed at the accurate position on the flat plate.
The third object of the invention can be attained by a magnetic tape cassette which comprises an ID board for enabling a hardware to identify the magnetic tape by bringing contacts on a circuit board which is exposed through an opening formed in a lower cassette half into contact with corresponding contacts in the hardware, characterized in that a plating treatment is provided on the contacts on the ID board, and that a determined distance is secured between all end portions of the parts provided with the plating treatment and end faces of the circuit board.
In the magnetic tape cassette according to the invention, the ID board enables the hardware to identify the type or the use of the magnetic tape by bringing the contacts on the board exposed through an opening which is formed in the lower cassette half into contact with the corresponding contacts in the hardware. The plating treatment is provided on the contacts of the ID board. Because a determined distance is secured between the end portions of the plated parts and the end faces of the board, a stamping cutter will not abut against the plated parts when the board is stamped by means of a press. Accordingly, the burrs and damages will not be generated on the plated parts and shorts of the contacts by a metal piece can be prevented beforehand.
In this case, all the end portions of the plated parts means entire peripheral edges of the plated parts, and in case where the rectangular parts are plated as shown in FIG. 21, all the four edges of each the rectangular part are meant. The end face of the board means a face around the board which is substantially perpendicular to a direction of a plane of the board.
From a view point of preventing the occurrence of the burrs which may be a cause of the shorts, the distance had better be as large as possible. However, as shown in FIG. 23, the magnetic tape cassette 50 is loaded in the hardware 43 while the plated parts 36 of the ID board 33 are slid in a direction of an arrow C with respect to the corresponding contacts 44 of the hardware. Accordingly, in case where the distance is too large, it may happen that the exposed parts of the ID board 33 (those parts not plated) will get to slidingly contact with the contacts 44 and a reliable detection of the contact will be impossible. Therefore, the distance at the forward end in the sliding direction of the arrow C among these distances is preferably 0.25 mm or less in view of electrically stable detection of the contacts.
Meanwhile, having earnestly studied and examined the burrs or damages in question with respect to size, their sizes were found to be between about 0.02-0.1 mm.
Therefore, considering stability of the above described contact detection and variations in working precision, the distance at the forward end is 0.05-0.25 mm and preferably 0.1-0.15 mm.
The fourth object of the invention can be attained by a magnetic tape cassette which comprises a cassette case consisting of an upper and a lower cassette halves, a pair of tape reels around which a magnetic tape contained in the cassette case is wound, and an openable lid fitted to the cassette case so as to cover an opening along which the magnetic tape arranged at a front side of the cassette case is adapted to pass, characterized in that side faces of the cassette case are provided with cut away portions so that forward ends of the side faces of the cassette case maybe always located closer to an inner space of the cassette case than side faces of the openable lid.
According to the above described structure of the invention, even in case where the cassette is loaded in a cassette loading mouth with the openable lid displaced toward one side and inclinedly with respect to the cassette loading mouth, the cassette will not be caught and can be smoothly guided into the interior of the hardware, because the forward ends of the side faces of the cassette case may be always located closer to the inner space of the cassette case than the side faces of the openable lid due to the presence of the cut away portions. Therefore, the magnetic tape cassette can be smoothly loaded in the hardware.
The cut away portion may be of a tapered or a curved shape.